1. Field of the Invention
The present invention relates, generally, to an automotive seat assembly and, more specifically, to a seat assembly that employs a self-clearing drive nut used cooperatively with a lead screw in an adjustable seat drive mechanism.
2. Description of the Related Art
Seat assemblies having power seat adjusters are a popular component in many automotive vehicles. It is known to use power seat adjusters to provide powered horizontal fore and aft adjustment of the vehicle seat, as well as to use power seat adjusters to provide vertical adjustments to raise and lower the seat height. Separate front and rear seat elevation mechanisms have also been employed to independently, as well as simultaneously, adjust the elevation of the front and rear edges of a vehicle seat. Power seat recliners have also been incorporated into power seat adjusters.
Typically, a vehicle power seat adjuster includes a support frame or support members that engage and support the bottom of a vehicle seat. The seat support members are mounted on spaced track assemblies that form a movable frame portion. In turn, the moveable frame portion is slidably mounted in a main track or main support portion of the seat frame that is anchored to the floor pan of the vehicle.
A drive mechanism rotates a threaded lead screw that extends between the movable portion and the fixed main portion of the seat frame. The drive mechanism is typically a bi-directional electric motor mounted between the main and movable frame portions. Often, two lead screws are used, one on each side of the seat frame, to provide smooth fore and aft movement. In these applications, the motor has two drive shafts each driving a separate gear assembly or gearbox, each gearbox further connected to the individual lead screws. This can provide torque multiplication, speed reduction, or both, to the lead screw as may be required for the particular application.
If the drive motor is mounted on the main portion of the seat frame, then a drive block or drive nut is fixedly connected to the movable frame portion. The drive nut has an internally threaded through-bore that receives the threaded lead screw. This allows selective control of the motor to effect reciprocal movement of the movable frame portion in a fore and aft direction relative to the main portion of the seat frame. Also, in some applications, the motor may be mounted on the movable portion with the drive nuts fixed to the main portion of the seat frame.
To allow for vertical movement of the front and back ends of the seat, a similar drive motor, gear box, and threaded lead screw drive are mounted between the main frame portion and a second movable frame portion that is operatively hinged to the main portion of the seat frame. Some more sophisticated seat drive mechanisms also employ additional drive motors, lead screws and drive nuts, to allow for the control of pivotal movement of the seat back with respect to the seat bottom. While the seat drive mechanisms of the type generally known in the related art work well as initially installed, they are prone to certain operational complications over time that impact the drive mechanism's ability to properly function. This occurs due to the general operating environment in which the seat drive mechanisms must function.
The threaded interaction between each of the lead screws and their respective drive nuts must be clean and lubricated in order to ensure proper and repeatable operation. Due to the length and travel range of the lead screws, they must remain open to their surrounding environment under the vehicle seat. It has proven impractical to attempt to encase or enclose the lead screw and drive nut assemblies. On the other hand, the physical area under the seats of most vehicles ultimately becomes cluttered and generally unclean. In fact, the under seat area is prone to collecting dust and dirt just through normal use of a motor vehicle and also becomes a receptacle for all manner of objects. The nature of this operating environment introduces a wide variety of foreign objects to the threads of the lead screws. This means that as the lead screws sit, they collect all manner of debris in their threads. Then, as the seat drive mechanisms are operated, the male threads of the lead screws carry this foreign matter into the cooperative female threads of the drive nut. The introduction of foreign matter to the threaded interaction of the lead screw and the drive nut may cause binding, slow and labored operation, and ultimately jamming of the seat drive mechanism.
In response to this problem, some corrective measures have been attempted in the related art with limited success. It is known to construct a drive nut that is made of a plastic, or nylon-type material that is somewhat soft and self-lubricating. The self-lubrication nature of these types of materials avoid having to apply a separate lubricating media to the lead screw, which reduces some collection of foreign matter on the lead screw, but does not eliminate it. Drive nuts made of these soft and somewhat giving materials can also tolerate some amount of foreign material stuck in their threads before a binding condition occurs, but again, this does not eliminate the problem. It is also known to thread the lead screws and their respective drive nuts with an “Acme” thread profile. This specific thread configuration generally provides for a closer tolerance fit between the male threads of the lead screw and the female threads of the drive nut at the entry thread area and reduces the tolerance gap at the thread crest and root interface area. Both of these changes reduce the opportunity for foreign matter to enter into the threads. However, this only slows the onset of a binding or jamming condition and does not eliminate the problem.
Therefore, there remains a need in the art for a seat assembly that employs a drive nut that is capable of a maintaining a proper threaded interaction with a lead screw but avoids the binding and jamming condition that occurs by the introduction of foreign matter to the drive nut threads from the lead screw threads.